Compact and reliable structure of multi-rotor synchronous machine

ABSTRACT

A compact and reliable structure of a multi-rotor synchronous machine which may be employed as a generator/motor for automotive vehicles is provided. The machine includes an outer rotor having permanent magnets, an inner rotor having permanent magnets disposed to be rotatable relative to the outer rotor, a stator core having armature coils interlinking with field magnetic fluxes produced by the outer and inner rotors, and a rotor-to-rotor relative rotation controlling mechanism. A relative angle between the outer and inner rotors is controlled within a given angular range by controlling the phase and quantity of current flowing through the armature coils to rotate the inner rotor relative to the outer rotor through the rotor-to-rotor relative rotation controlling mechanism, thereby changing the magnetic fluxes interlinking with the armature coils as needed.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] The present invention relates generally to a multi-rotorsynchronous machine which may be used as a generator/motor forautomotive vehicles such as hybrid vehicles, and more particularly to acompact and reliable structure of a multi-rotor synchronous machine.

[0003] 2. Background Art

[0004] Typical permanent magnet synchronous machines are capable ofproducing a higher output and have the structure easy to reduce in sizeas compared with other types of synchronous machines and thus suitablefor use as driving motors of hybrid vehicles or electric vehicles.However, increasing a magnet-produced magnetic field in such a drivingmotor in order to ensure a sufficient torque during rotation of themotor at low speeds causes an excessive armature winding-induced voltageto be applied to semiconductor elements of a driving circuit duringrotation at high speeds undesirably. In order to avoid this problem, anymeans is needed which is designed to reduce the magnetic field producedduring rotation of the motor at high speeds.

[0005] U.S. Pat. No. 5,955,807 (Japanese Patent First Publication No.10-304633), issued on Sep. 21, 1999, assigned to the same assignee asthat of this application teaches a stationary field coil/magnetsynchronous machine which includes permanent magnets installed in arotor core, magnetically coupling members inserted into the rotor corein an axial direction thereof to short-circuiting the permanent magnetsmagnetically, a stationary yoke installed inside the rotor core, fieldcoils provided around the rotor core. The synchronous machine works toenergize the field coils to regulate the quantity of magnetic fluxflowing through the magnetically coupling members to control aneffective quantity of magnetic flux interlinking with the armaturewindings, thereby regulating the voltage generated by the armaturewindings.

[0006] EP 0901923 A2 discloses an automotive rear-mounted motorgenerator which is disposed between a crankshaft and a transmission anddriven by the crankshaft. The user of the rear-mounted motor generatorallows auxiliary mechanical parts to be mounted along a belt in front ofthe engine which also serve to minimize the slippage of the belt on asmall-diameter pulley for driving the motor generator.

[0007] The synchronous machine, as taught in the former document, has aproblem that the structure is complex.

[0008] The motor generator, as taught in the latter document, encountersdrawbacks in that the mounting of the motor generator between thecrankshaft and the transmission installed behind the crankshaft causesthe overall length of the power train to be increased, thus resulting inincreases in size and weight of an assembly of the power train and itscover and also results in a difficulty in ensuring the rigiditysufficient to resist mechanical vibrations and deformation of the powertrain.

SUMMARY OF THE INVENTION

[0009] It is therefore a principal object of the invention to avoid thedisadvantages of the prior art.

[0010] It is another object of the invention to provide a compactstructure of a multi-rotor synchronous machine designed to operateselectively in a motor mode and a generator mode with high reliabilitylevels.

[0011] According to one aspect of the invention, there is provided amulti-rotor synchronous machine which may be employed in agenerator/motor for automotive vehicles. The multi-rotor synchronousmachine includes: (a) a fist rotor having permanent magnet field poles,secured to an output member; (b) a second rotor having permanent magnetfield poles, disposed to be rotatable relative to the first rotor; (c) astator core having armature coils interlinking with field magneticfluxes produced by the permanent magnet field poles of the first andsecond rotors; and (d) a rotor-to-rotor relative rotation controllingmechanism designed to allow the second rotor to rotate relative to thefirst rotor within a given angular range and prohibit the second rotorfrom rotating out of the given angular range.

[0012] In the preferred mode of the invention, the rotor-to-rotorrelative rotation controlling mechanism includes a first stopper workingto limit rotation of the second rotor relative to the first rotor in afirst direction over a first angular range and a second stopper workingto limit rotation of the second rotor relative to the first rotor in asecond direction opposite the first direction over a second angularrange.

[0013] The rotor-to-rotor relative rotation controlling mechanismincludes an elastic member which is engagement at one end thereof withthe first rotor and at the other end with the second rotor to urge thefirst and second rotors in opposite directions.

[0014] The stator core is made of a hollow cylindrical member. The firstrotor and the second rotor are disposed coaxially with an outer and aninner periphery of the stator core, respectively.

[0015] The second rotor is disposed inside the inner periphery of thestator core. The rotor-to-rotor relative rotation controlling mechanismis installed inside the second rotor.

[0016] The rotation of the second rotor relative to the first rotor isaccomplished by controlling at least one of phase and quantity ofcurrent flowing through the armature coils of the stator core.

[0017] According to another aspect of the invention, there is provided amulti-rotor synchronous machine which comprises: (a) a pair of rotors atleast one of which has permanent magnet field poles, the rotors beingarrayed coaxially to be rotatable relative to each other; (b) a statorcore; (c) armature coils wound in the stator core, interlining with afield flux produced by the rotors; (d) a sensor measuring a relativeangle between the rotors; and (e) a rotor-to-rotor relative anglecontroller working to establish a relative rotation between the rotorsto change the relative angle measured by the sensor to a target angle.

[0018] In the preferred mode of the invention, the stator core is madeof a hollow cylindrical member. The rotors are an outer rotor disposedaround an outer periphery of the stator core and an inner rotor disposedaround an inner periphery of the stator core. The rotor-to-rotorrelative angel controller includes a relative rotation controllingmechanism disposed inside the inner rotor for controlling a relativerotation between the rotors.

[0019] The relative rotation controlling mechanism includes an elasticmember laid between the rotors in a circumferential direction thereof tokeep the rotors in a neutral position. The rotor-to-rotor relative anglecontroller changes magnetic torques acting on the rotors to adjust arelative angle between the rotors to a target angle.

[0020] The rotor-to-rotor relative angle controller is designed tochange the magnetic torque acting on the rotors to rotate one of therotors relative to the other from the neutral position while compressingor expanding the elastic member, thereby adjusting the relative anglebetween the rotors to the target angle.

[0021] The relative rotation controlling mechanism includes a pair ofelastic members secured on one of the rotors to establish the neutralposition in which the rotors have a preselected angular relationtherebetween when the armature coils is deenergized. The rotor-to-rotorrelative angle controller changes the magnetic torques acting on therotor to cause one of the elastic members to be compressed whileexpanding the other elastic member, thereby adjusting the relative anglebetween the rotors to the target angle.

[0022] The relative rotation controlling mechanism includes a pair ofstoppers working to define a relative rotation allowable range of therotors.

[0023] When the rotors are in a first relative angular position lyingone of limits of the relative rotation allowable range defined by one ofthe stopper, a maximum torque is produced on the rotors in a directionof rotation of the multi-rotor synchronous machine. When the rotors arein a second relative angular position lying the other limit of therelative rotation allowable range defined by the other stopper, amaximum torque is produced on the rotors in a direction reverse to thedirection of rotation of the multi-rotor synchronous machine.

[0024] One of the rotors has an inertial mass two times greater thanthat of the other rotor or more.

[0025] One of the rotors having the greater inertial mass is coupled toa crankshaft of an automotive engine. The other rotor is coupled to theone of the rotors through the rotor-to-rotor relative angle controllerto be rotatable relative to the one of the rotors.

[0026] The relative rotation controlling mechanism establish anengagement between the rotors so as to allow the rotors to rotaterelative to each other continuously in a given angular range.

[0027] According to the third aspect of the invention, there is provideda drive apparatus for an automotive vehicle which comprises: (a) aflywheel connected to a rear end of a crankshaft of an engine; (b) agenerator/motor includes a stator which is located in front of theflywheel and secured to a housing and a rotor which is secured on theflywheel and faces a peripheral surface of the stator; and (c) amechanical clutch establishing an engagement between the flywheel and aninput shaft of a gear reduction unit disposed behind the flywheel, theinput shaft extending through the flywheel coaxially with thecrankshaft.

[0028] The mechanical clutch includes, (a) a pressure plate supported bythe flywheel nonrotatably and slidably in an axial direction of theinput shaft of the gear reduction unit, the pressure plate facing a rearsurface of the flywheel through a given gap, (b) a clutch platesupported by the input shaft nonrotatably and slidably in the axialdirection, the clutch plate being disposed between the rear surface ofthe flywheel and a front surface of the pressure plate, (c) an annularclutch spring located behind the pressure plate, supported by theflywheel so as to urge at an outer periphery thereof a rear end surfaceof the pressure plate frontward, (d) a sleeve fitted on the input shaftthrough a given gap between itself and an outer peripheral surface ofthe input shaft, the sleeve being located behind the clutch plate andsecured at a rear end thereof to the housing, (e) a release pistonfitted on the outer peripheral surface of the sleeve slidably in anaxial direction of the sleeve, and (f) a release bearing fitted on therelease piston or the sleeve to be movable in the axial direction tourge an inner peripheral portion of the clutch spring.

[0029] The flywheel includes a small-diameter cylinder coupled at afront end thereof to the rear end of the crank shaft and a discextending from a rear end of the small-diameter cylinder in acentrifugal direction to be engageble with the clutch plate. The clutchplate includes a cylinder which has a chamber opened rearward into whichthe release bearing is allowed to be inserted at least partially andwhich is fitted on the input shaft nonrotatably and slidably in theaxial direction and a disc extending from a rear end of the cylinderbetween the rear end surface of the flywheel and the front end surfaceof the pressure plate. At least a portion of the release piston and therelease bearing are located frontward of the clutch spring.

[0030] In the preferred mode of the invention, the release bearing isfitted on the release piston.

[0031] The clutch plate includes a clutch damper located between thecylinder and the disc thereof for absorbing a variation in torque. Afront portion of the clutch damper is disposed within a chamber formedin a rear end portion of the cylinder of the flywheel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be understood more fully from thedetailed description given hereinbelow and from the accompanyingdrawings of the preferred embodiments of the invention, which, however,should not be taken to limit the invention to the specific embodimentsbut are for the purpose of explanation and understanding only.

[0033] In the drawings:

[0034]FIG. 1 is a partially sectional view which shows a multi-rotorsynchronous machine according to the first embodiment of the invention,as taken along an axial direction thereof;

[0035]FIG. 2 is a partially sectional view which shows the multi-rotorsynchronous machine of FIG. 1, as taken along a broken line C in FIG. 1;

[0036]FIG. 3 is a partially sectional view which shows the multi-rotorsynchronous machine of FIG. 1 when used as a torque assist motor forautomotive vehicles;

[0037]FIG. 4 is a graph which shows the relation between the phase ofcurrent flowing through armature coils and torques acting on outer andinner rotors;

[0038]FIG. 5 is a graph which represents the relation between the phaseof current supplied to armature coils and an output torque when anangular difference between outer and inner rotors is near zero;

[0039]FIG. 6 is a graph which represents the switching between alow-torque mode as shown in FIG. 2 and a high-torque mode as shown inFIG. 3 across a point where electromagnetic force is balanced withelastic pressure;

[0040]FIG. 7 is a partially sectional view which shows a modification ofa multi-rotor synchronous machine of the first embodiment;

[0041]FIG. 8 is a partially sectional view which shows a multi-rotorsynchronous machine according to the second embodiment of the invention,as taken along an axial direction thereof;

[0042]FIG. 9 is a partially sectional view which shows the multi-rotorsynchronous machine of FIG. 8, as taken along a radius directionthereof;

[0043]FIG. 10 is a partially enlarged view which shows arrangements ofelastic members and ribs of a rotor support stay and an inner rotorsupport stay;

[0044]FIG. 11 is a graph which shows the relation between loads actingon an inner rotor and relative angle between the inner and outer rotors;

[0045]FIG. 12 is a partially sectional view which shows the phase ofcurrent flowing through armature coils which is controlled when it isrequired to change the relative angle between outer and inner rotorsfrom that in a neutral position in the second embodiment;

[0046]FIG. 13 is an illustration which shows torques acting on outer andinner rotors when the phase of current flowing through armature coils iscontrolled as shown in FIG. 12;

[0047]FIG. 14 is a graph which shows the relation between torques actingon outer and inner rotors when the phase of current flowing througharmature coils is controlled as shown in FIG. 12;

[0048]FIG. 15 is a sectional view which shows the phase of currentflowing through armature coils controlled in a low-speed and high torquemotor mode in the second embodiment;

[0049]FIG. 16 is an illustration which shows torques acting on outer andinner rotors when the phase of current flowing through armature coils iscontrolled as shown in FIG. 15;

[0050]FIG. 17 is a sectional view which shows the phase of currentflowing through armature coils controlled in a high-speed low-torquemotor mode in the second embodiment;

[0051]FIG. 18 is an illustration which shows torques acting on outer andinner rotors when the phase of current flowing through armature coils iscontrolled as shown in FIG. 17;

[0052]FIG. 19 is a sectional view which shows the phase of currentflowing through armature coils controlled in a high-speed low-torquegenerator mode in the second embodiment;

[0053]FIG. 20 is an illustration which shows torques acting on outer andinner rotors when the phase of current flowing through armature coils iscontrolled as shown in FIG. 19;

[0054]FIG. 21 is a sectional view which shows the phase of currentflowing through armature coils controlled to change the relative anglebetween outer and inner rotors for establishing a high-torque generatormode in the second embodiment;

[0055]FIG. 22 is an illustration which shows torques acting on outer andinner rotors when the phase of current flowing through armature coils iscontrolled as shown in FIG. 21;

[0056]FIG. 23 is a sectional view which shows the phase of currentflowing through armature coils controlled in a high-torque generatormode in the second embodiment;

[0057]FIG. 24 is an illustration which shows torques acting on outer andinner rotors when the phase of current flowing through armature coils iscontrolled as shown in FIG. 23;

[0058]FIG. 25 is a flowchart of a program to be performed to operate amulti-rotor synchronous machine at the start-up of the engine.

[0059]FIG. 26 is a flowchart of a program to be performed to operate amulti-rotor synchronous machine in a regenerative braking mode;

[0060]FIG. 27 is a sectional view which shows a multi-rotor synchronousmachine according to the third embodiment of the invention;

[0061]FIG. 28 is a graph which shows the relation between the speed ofthe synchronous machine of FIG. 27 and the produced torque in the thirdembodiment;

[0062]FIG. 29 is a sectional view which shows a positional relationbetween outer and inner rotors in a low-speed high-torque motor mode inthe third embodiment;

[0063]FIG. 30 is a sectional view which shows a positional relationbetween outer and inner rotors in a high-speed low-torque motor mode;

[0064]FIG. 31 is a sectional view which shows a positional relationbetween outer and inner rotors in a low-speed high-torque generator modein the third embodiment;

[0065]FIG. 32 is a graph which shows the relation between the amount ofexpansion of an elastic member and a load acting on the elastic memberin the third embodiment of the invention;

[0066]FIG. 33 is a sectional view which shows a multi-rotor synchronousmachine according to the fourth embodiment of the invention;

[0067]FIG. 34 is a sectional view, as developed in a circumferentialdirection of a multi-rotor synchronous machine, which shows an outerrotor-to-inner rotor relative angle adjusting structure according to thefourth embodiment of the invention;

[0068]FIG. 35 is a sectional view which shows a multi-rotor synchronousmachine operating in a generator mode;

[0069]FIG. 36 is a sectional view which shows a multi-rotor synchronousmachine operating in a motor mode;

[0070]FIG. 37 shows a graph which represents the relation between theamount of expansion of elastic members and produced torque:

[0071]FIG. 38 is a sectional view which shows the part of an automotivepower train according to the fifth embodiment of the invention in whicha multi-rotor synchronous machine is installed as a generator/motor; and

[0072]FIG. 39 is a partially sectional view which shows a connection ofa clutch spring to a hydraulic pressure releasing mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0073] Referring to the drawings, wherein like reference numbers referto like parts in several views, particularly to FIGS. 1 and 2, there isshown a multi-rotor synchronous machine according to the firstembodiment of the invention. The following discussion will refer to anexample in which the multi-rotor synchronous machine is used as a dynamoelectric machine or generator/motor for automotive vehicles such ashybrid vehicles.

[0074] The synchronous machine includes generally a stator 210, an outerrotor 220, an inner rotor 230, a rotor support frame 240, and a statorsupport frame 250.

[0075] The stator 210 consists of a hollow cylindrical stator core 211disposed within an annular gap between the outer rotor 220 and the innerrotor 230 coaxially therewith and armature coils 212 magneticallycoupling with the rotors 220 and 230.

[0076] The stator core 211 is made of a lamination of a plurality ofmagnetic discs laid to overlap each other in an axial direction of thesynchronous machine. The stator core 211, as clearly shown in FIG. 2,has outer slots 213 formed in an outer wall thereof at regular intervalsin a circumferential direction and inner slots 213′ formed in an innerwall thereof in the circumferential direction at regular intervals. Eachof the outer slots 213 is, as can be seen in FIG. 2, aligned with one ofthe inner slots 213′ in a radius direction of the stator core 211. Inother words, each of the outer slots 213 is provided at the samelocation in the circumferential direction of the stator core 211 as thatof one of the inner slots 213′. A tooth 214 is defined between adjacenttwo of the outer slots 213. Similarly, a tooth 214′ is defined betweenadjacent two of the inner slots 213′. A core back 215 is defined betweenthe outer slots 213 and the inner slots 213′. The stator core 211 hasholes 216 extending through the core back 215 in the axial direction.The stator core 211 is secured on an inner periphery of the statorsupport frame 250 through bolts 252 screwed into the holes 216. Thestator support frame 250 is made of a ring-shaped plate on which anannular step is formed and attached at an outer periphery thereof to ahousing (not shown) in front of and outside the stator core 211 in aradius direction of the stator core 211.

[0077] The armature coils 212 are made of as many toroidal windings asthe outer slots 213 (i.e., the inner slots 213′). Each of the toroidalwindings is formed by a conductor wound through one of the outer slots213 and a corresponding one of the inner slots 213′ which are arrayed atthe same angular position in the circumferential direction of the statorcore 211. Leading and trailing ends of each of the toriodal windingsextend outside the front end of the stator core 211. The leading andtrailing ends of the toroidal windings are broken into three groups andconnected in the respective groups to provide three-phase windings: aU-phase winding, a V-phase winding, and a W-phase winding. In thisembodiment, the U-phase winding is wound through nth pairs of the slots213 and 213′ in the circumferential direction of the stator core 211.The V-phase winding is wound through (n+1)th pairs of the slots 213 and213′. The W-phase winding is wound through (n+2)th pairs of the slots213 and 213′. The armature coils 212 are connected electrically to acontroller 500. The controller 500 works to control the phase andquantity of current flowing through the armature coils 212.

[0078] The outer rotor 220 and the inner rotor 230 are each made of ahollow cylindrical member. The inner peripheral surface of the outerrotor 220 is magnetically coupled with an outer peripheral surface ofthe inner rotor 230 through a small magnetic gap. The outer rotor 220includes a soft iron-made hollow cylinder 222 and permanent magnets 221each made of a magnetic plate curved along the circumference of thehollow cylinder 222. The permanent magnets 221 are arrayed on the innerwall of the hollow cylinder 222 at regular intervals in thecircumferential direction thereof. Similarly, the inner rotor 230includes a soft iron-made hollow cylinder 232 and permanent magnets 231each made of a magnetic plate curved along the circumference of thehollow cylinder 232. The permanent magnets 231 are arrayed on the outerwall of the hollow cylinder 232 at regular intervals in thecircumferential direction thereof. The permanent magnets 221 aremagnetized in the radius direction of the hollow cylinder 222 and soarranged that different field poles, i.e., N-poles and S-poles arearrayed alternately in the circumferential direction of the hollowcylinder 222. Similarly, the permanent magnets 231 are magnetized in theradius direction of the hollow cylinder 232 and so arranged that N-polesand S-poles are arrayed alternately in the circumferential direction ofthe hollow cylinder 232.

[0079] The rotor support frame 240 includes an outer hollow cylinder2401, an inner hollow cylinder 2402, and an annular disc 2403. The outerhollow cylinder 2401 retains the outer periphery of the outer rotor 220.The inner hollow cylinder 2402 supports the inner surface of the innerrotor 230 rotatably in the circumferential direction thereof. Theannular disc 2403 connects rear ends of the outer hollow cylinder 2401and the inner hollow cylinder 2401 together. The inner hollow cylinder2402 is coupled at a front end thereof to a rear end of a crankshaft 110of the engine (not shown). The annular disc 2403 is coupled at a rearend thereof to a transmission (not shown) through a clutch mechanism(not shown). An example of the connection of the multi-rotor synchronousmachine with the engine and the transmission will be described in detaillater with reference to FIGS. 38 and 39.

[0080] A support structure for the inner rotor 230 will be describedbelow.

[0081] A hollow cylinder 234 serving as an inner rotor support stay ispress fit in the inner rotor 230. The hollow cylinder 234 has formed onan inner wall thereof at regular intervals in a circumferentialdirection a plurality of protrusions or ribs 2341 each extending in aradius direction. A pair of ball bearings 235 and 236 is mounted on theinner cylinder 2402 of the rotor support frame 240. The inner cylinder2402 has formed on an outer wall thereof in a circumferential directionhigher and lower ribs 24021 and 24022 which extend in a radius directionof the inner cylinder 2402 and are arrayed alternately at regularintervals in the circumferential direction thereof. An arc-shapedelastic member 238 such as rubber is installed between each of the ribs2341 and one of the ribs 24021 located adjacent that rib 2341 in aclockwise direction as viewed in FIG. 2.

[0082] Specifically, the inner rotor support stay 234 and the innerrotor 230 secured on the inner rotor support stay 234 are so constructedas to be rotatable relative to the outer rotor 220 within a range of anangular position where each of the ribs 2341 is in contact with one ofthe ribs 2341 to an angular position where the torque acting on the rib2341 is balanced with the elastic pressure produced by one of theelastic members 238.

[0083] Each of the elastic members 238 is in contact at a left end, asviewed in FIG. 2, with one of the ribs 2341 and at a right end with oneof the ribs 24021 to urge the rib 2341 against a corresponding one ofthe ribs 24022 in a counterclockwise direction.

[0084] In operation, the location of the field pole of the outer rotor220 is monitored to determine the phase and frequency of a three-phasealternating voltage to be applied to the armature coils 212 forproducing the torque. This operation is the same as that of typicalpermanent magnet field pole synchronous machines, and explanationthereof in more detail will be omitted there.

[0085] The adjustment of an angular position of the inner rotor 230relative to the outer rotor 220 will be described below with referenceto FIGS. 2 and 3, taking an example wherein the multi-rotor synchronousmachine is operated in a motor mode (i.e., a torque assist mode usuallyused in hybrid vehicles). It the following discussion, it is assumedthat when the ribs 2341 of the inner rotor support stay 234 are in theleftmost angular position in the counterclockwise direction, asillustrated in FIG. 2, that is, when the inner rotor 230 is shiftedrelative to the outer rotor 220 and lies at a counterclockwise angularlimit, the elastic members 238 work to urge the inner rotor 230elastically in the counterclockwise direction at a minimum elasticpressure. FIG. 3 illustrates the inner rotor 30 which is shiftedrelative to the outer rotor 220 in the clockwise direction to therightmost angular position and lies at a clockwise angular limit.

[0086] In the angular position of FIG. 2, the inner rotor 230 is urgedby the elastic members 238 in the counterclockwise direction and held atthe counterclockwise angular limit. Specifically, the ribs 2341 of theinner rotor support stay 234 are pressed by the elastic members 238 intoconstant engagement with the ribs 24022 of the inner cylinder 2402. Ifthe electromagnetic force produced in the motor mode acting on the innerrotor 230 in the clockwise direction is less than a lower limit of theelastic pressure provided by the elastic members 238, the inner rotor230 are held at the illustrated angular position.

[0087] The setting of the electromagnetic force acting on the innerrotor 230 to the lower limit of the elastic pressure provided by theelastic members 238 or less is accomplished by adjusting either or bothof the quantity and phase of current flowing through the armature coils212 using the controller 500. The magnitude of the electromagneticforces acting on the outer and inner rotors 220 and 230 depend upon thephase and quantity of current flowing through the armature coils 212.Accordingly, when there is the angular difference, as shown in FIG. 2,between the outer rotor 220 and the inner rotor 230, the sum of themotor torques produced by the outer and inner rotors 220 and 230, i.e.,the resultant output torque will be small. Specifically, the quantity ofresultant field magnetic flux interlinking with the armature coils 212is small, so that the counter electromotive force produced in thearmature coils 212 during rotation of the synchronous machine at highspeeds will be low. FIG. 4 represents an example of torquecharacteristics when a greater angular difference is established betweenthe outer rotor 220 and the inner rotor 230. Note that theelectromagnetic force acting on the inner rotor 230 is outputted throughthe elastic members 238.

[0088] As the electromagnetic force acting on the inner rotor 230 (i.e.,the electromagnetic force oriented in the clockwise direction)increases, a balance point at which the electromagnetic force balanceswith the elastic pressure of the elastic members 238 is shifted in theclockwise direction, as viewed in FIG. 2, thereby causing the angularposition of the inner rotor 230 relative to the outer rotor 220 to beshifted in the clockwise direction. The increasing of theelectromagnetic force acting on the inner rotor 230 is accomplished byincreasing the quantity of current flowing through the armature coils212 and/or controlling the phase thereof. The clockwise rotation of theinner rotor 230 relative to the outer rotor 220 causes the phasedifference between vectors of torques of the outer and inner rotors 220and 230 to decrease, thus resulting in an increase in resultant motortorque.

[0089] A more increase in electromagnetic force acting on the innerrotor 230 in the clockwise direction causes the balance point of theelectromagnetic force and the elastic pressure developed by the elasticmembers 238 to be shifted in the clockwise direction further, so thatthe inner rotor 230 moves relative to the outer rotor 220 toward theclockwise angular limit (i.e., the rightmost angular position in FIG.2). When the inner rotor 230 reaches the clockwise angular limit, asshown in FIG. 3, and the electromagnetic force acting on the inner rotor230 exceeds an upper limit of the elastic pressure developed by theelastic members 238, it will cause the inner rotor 230 to be held at theangular position as illustrated in FIG. 3. In this position, a near zeroangular difference is established between the permanent magnets 221 and231 of the outer rotor 220 and the inner rotor 230, so that a greatfield magnetic flux acts on the armature coils 212, thereby allowing agreater motor torque to be outputted. FIG. 5 represents a torquecharacteristic when the angular difference between the outer rotor 220and the inner rotor 230 is almost zero. The shift of the inner rotor 230from the angular position of FIG. 3 to that of FIG. 2 is accomplished bydecreasing the quantity of current flowing through the armature coils212 and controlling the phase thereof in a manner reverse to that asdescribed above to decrease the electromagnetic force acting on theinner rotor 230.

[0090] As apparent from the above discussion, when the electromagneticforce produced in the motor mode acting on the inner rotor 230 is lessthan the lower limit of the elastic pressure produced by the elasticmembers 238 or when the electromagnetic force is produced in thecounterclockwise direction, as viewed in FIG. 2, in the generator mode,the inner rotor 230 is held at the angular position as illustrated inFIG. 2. When the electromagnetic force acting on the inner rotor 230 isequal to the elastic pressure produced by the elastic members 238, theinner rotor 230 is held intermediate between the angular positions inFIGS. 2 and 3. When the electromagnetic force acting on the inner rotor230 is greater than the upper limit of the elastic pressure produced bythe elastic members 238, the inner rotor 230 is held at the angularposition as illustrated in FIG. 3. Therefore, when it is required forthe synchronous machine to produce a greater torque at low speeds, forexample, in a start-up mode of engine operation, the synchronous machineis preferably operated with the inner rotor 230 held at the angularposition as illustrated in FIG. 3. When it is required to run thesynchronous machine at high speeds, the inner rotor 230 is preferablyheld at the angular position as illustrated in FIG. 2, therebydecreasing the counterelectromotive force produced in the armature coils212. FIG. 6 shows an example of an output torque control mode in whichwhen a required motor torque exceeds a threshold level X, the innerrotor 230 is switched from the angular position as illustrated in FIG. 2to that as illustrated in FIG. 3. The inner rotor 230 may also be heldat the intermediate angular position as a function of the magnitude ofthe required motor torque.

[0091] Specifically, the inner rotor 230 is retained to be rotatablerelative to the outer rotor 220. The inner rotor 220, thus, produces thetorque varying as a function of an angular position relative to theouter rotor 220.

[0092] As apparent from the above discussion, in a case where themulti-rotor synchronous machine is used as an automotivegenerator/motor, when it is required to use the generator/motor forassisting in outputting the drive torque, the reduction incounterelectromotive force induced in the armature coils 212 may beachieved by adjusting the magnitude or phase of current to be suppliedto the armature coils 212. If a failure in control of an inverter occurswhen the automotive vehicle is running at high speeds, a great voltageis not developed at the armature coils 212, thus improving the safety ofa power source system. Specifically, when the automotive vehicle isrunning at high speeds, the inner rotor 230 is held at the angularposition as illustrated in FIG. 2. Thus, if the failure in control ofthe inverter occurs, the resultant field magnetic flux interlinking withthe armature coils 212 is kept small, thereby keeping induced openelectromotive voltage at a lower level.

[0093]FIG. 7 shows a modification of the multi-rotor synchronous machineof the first embodiment which may be employed as a drive generator/motorinstalled in a fuel cell-powered vehicle.

[0094] The multi-rotor synchronous machine includes a stator 1, an outerrotor 2, an inner rotor 3, a rotor support frame 4, and a stator supportframe 5. The stator 1 and the outer and inner rotors 2 and 3 areidentical in structure with the stator 210 and the outer and innerrotors 220 and 230 in the first embodiment.

[0095] The rotor support frame 4 includes a first plate 41 on which anouter periphery of the outer rotor 2 is mounted and a second plate 42 onwhich an inner periphery of the inner rotor 3 is mounted. The firstplate 41 is made up of an outer hollow cylinder 411 on which the outerperiphery of the outer rotor 2 is secured, a disc 412, and an innerhollow cylinder 413 fitted on a rotary shaft 100 nonrotatably. Thesecond plate 42 is made up of an outer hollow cylinder 421 on which theinner periphery of the inner rotor 2 is secured, a disc 422, and aninner hollow cylinder 423 fitted rotatably on the rotary shaft 100through a bearing metal 110.

[0096] A spring housing 111 is defined around a rear half of the innerhollow cylinder 423 and the inner hollow cylinder 413. A coil spring 200is disposed in the spring housing 111 and coupled at an end thereof tothe inner hollow cylinder 413 to urge the inner hollow cylinder 423 inthe counterclockwise direction like the first embodiment.

[0097] The inner hollow cylinder 413 has a groove 4130 formed in a frontend thereof over a given angular range. The inner hollow cylinder 423has formed on a rear end thereof a protrusion 4230 which extends intothe groove 4130. The protrusion 4230 is slidable in the groove 4130within a given angular range defined by contacts with ends of the groove4130 in a lengthwise direction thereof. This allows the inner rotor 3 torotate relative to the outer rotor 2 within the given angular range. Theinner rotor 3 is, as described above, urged elastically by the coilspring 200 in the counterclockwise direction as viewed from the frontside thereof, thereby producing the same effects as in the firstembodiment.

[0098]FIGS. 8 and 9 show a multi-rotor synchronous machine according tothe second embodiment of the invention. The same reference numbers asemployed in the first embodiment refer to the same parts, andexplanation thereof in detail will be omitted here.

[0099] Stator windings 212 (i.e., armature coils) are arrayed in amagnetic core 211 of a stator 210. Specifically, each stator winding 212consists of a conductor shaped to form a number of loops or turns eachof which extends from a front surface of the magnetic core 211 into oneof slots 213′ perpendicular to the drawing of FIG. 9 (i.e., a directionof lamination of magnetic discs making up the magnetic core 211), passesover a back surface of a core back 215, enters one of slots 213, andreturns back to a front surface of the magnetic core 211. The statorwindings 212 arrayed at a three-slot interval away from each other arecoupled to form one of three-phase windings.

[0100] The multi-rotor synchronous machine also includes, as shown inFIG. 9, an outer rotor 220 and an inner rotor 230. Magnets 221 and 231forming field poles are secured on rotor yokes 222 and 232. A rotorsupport stay 240 is connected to a crankshaft 110 of the engine. Themagnetic core 211 is installed on a stator support stay 250 through apin 252. The stay 250 is connected to an engine frame or transmission(not shown).

[0101] A inner rotor support stay 234 which retains the inner rotor 230is carried by bearings 235 and 236 to be slidable along the rotorsupport stay 240. An angle sensor 291 is installed on a back surface ofan end of the stator support stay 250 and monitors an angular positionof the inner rotor 230 relative to the outer rotor 220 to provide asignal indicative thereof. A pair of angle sensors may alternatively beinstalled on the stator support stay 250 to measure the angularpositions of the outer and inner rotors 220 and 230 independently.

[0102] First elastic members 238 such as springs or rubber are disposedaround the inside periphery of the rotor support stay 240. Each of thefirst elastic members 238 is secured at one end thereof to one ofprotrusions or ribs 240-1 formed on the inside periphery of the rotorsupport stay 240 and urges at the other end thereof one of spacers 249elastically in the counterclockwise direction, as viewed in FIG. 9. Thiscauses each of the spacers 249 to be urged, as clearly shown in FIG. 10,into constant engagement with one of protrusions or ribs 240-2 formed onthe inside periphery of the rotor support stay 240.

[0103] Second elastic members 239 such as springs or rubber are disposedaround the inside periphery of the rotor support stay 240. Each of thesecond elastic members 239 is secured at one end thereof to one ofprotrusions or ribs 240-3 formed on the inside periphery of the rotorsupport stay 240 and urges, as clearly shown in FIG. 10, at the otherend thereof one of protrusions or ribs 234-1 formed on an innerperiphery of the inner rotor support stay 234 in the clockwise directionas viewed in FIG. 9, so that the rib 234-1 elastically urges the spacer249 against the elastic pressure produced by the first elastic member238.

[0104] Stoppers 248-1 are each secured at one end thereof on the ribs240-1 of the rotor support stay 240. When the inner rotor support stay234 is rotated in the clockwise direction, as viewed in FIG. 9, the rib234-1 is brought into engagement with the other end of one of thestoppers 248-1, thereby defining a maximum clockwise angle of the innerrotor support stay 234.

[0105] Similarly, stoppers 248-2 are each secured at one end thereof onthe ribs 240-3 of the rotor support stay 240. When the inner rotorsupport stay 234 is rotated in the counterclockwise direction, as viewedin FIG. 9, the rib 234-1 is brought into engagement with the other endof one of the stoppers 248-1, thereby defining a maximumcounterclockwise angle of the inner rotor support stay 234.

[0106] Specifically, each of the ribs 234-1 of the inner rotor supportstay 234 is, as can be seen from FIG. 10, urged elastically by one ofthe first elastic members 238 in the counterclockwise direction and oneof the second elastic members 239 in the clockwise direction, so that itmay be movable between the stoppers 248-1 and 248-2 relative to therotor support stay 240.

[0107] The relation between the angular position of each of the ribs234-1 of the inner rotor support stay 234 relative to the rotor supportstay 240 (i.e., the relative angle between the outer and inner rotors220 and 230) and a load F1 produced by one of the first elastic member238 and a load F2 produced by one of the second elastic members 239acting on a corresponding one of the ribs 234-1 is shown in FIGS. 10 and11.

[0108] The operation of the multi-rotor synchronous machine of thisembodiment will be described below. It is assumed that when themulti-rotor synchronous machine is in an off-state, that is, when thearmature coils 212 are deenergized, the circumferential center of eachof the magnets 221 of the outer rotor 220 substantially coincides, asshown in FIG. 9, with that of a corresponding one of the magnets 231 ofthe inner rotor 230 in a radius direction, and different polarities ofthe magnets 221 and 231 are opposed to each other.

[0109]FIG. 12 shows a neutral position of the multi-rotor synchronousmachine. In this position, the magnets 221 of the outer rotor 220 areshifted an electrical angle of π from the magnets 231 of the inner rotor230, so that the armature coils 212 interlink with a resultant magneticflux that corresponds to a difference between magnetic fluxes of themagnets 221 and 231.

[0110] When the armature coils 212 are energized with the current ofphase as illustrated in FIG. 12, it will cause magnetic torque To to acton the outer rotor 220 and magnetic torque Ti to act on the inner rotor230. The magnetic torques To and Ti are oriented in opposite directions.

[0111] Specifically, if an elastic load (e.g., a spring load) producedby the elastic members 238 and an elastic load produced by the elasticmembers 239 are defined as F1 and F2, respectively, torque Tf, producedby a difference |F1−F2| opposed to the magnetic force oriented in thenormal direction of rotation of the synchronous machine acts on theinner rotor 230. Additionally, torque Tr produced by the elastic load F2opposed to the magnetic force oriented in the reverse direction ofrotation acts on the inner rotor 230. Assuming that the torque To isgreater than the torque Ti as a function of a difference in quantity ofmagnetic flux between the magnets 221 and 231, the torque Ti is greaterthan the torque Tf, and the torque Tf is substantially equal to thetorque Tr, these torques work to rotate the outer and inner rotors 220and 230 at angular accelerations of βo and βi from a start time t0 whenthe armature coils 212 start to be energized. Time-sequential changes inangular position of the outer and inner rotors 220 and 230 areillustrated in FIG. 14. If the inertial mass of the outer rotor 220 andthe inertial mass of the inner rotor 230 are defined as Io and Ii,respectively, relations between the torques and accelerations acting onthe outer and inner rotors 220 and 230 may be expressed as

To−Tf=Io·βo

Ti−Tf=Ii·βi

[0112] Since the inertial mass Io of the outer rotor 220 is muchgreater, preferably two times greater than the inertial mass Ii of theinner rotor 230 or more, the inner rotor 230 starts, as can be seen fromFIG. 14, to rotate more quickly than the outer rotor 220.

[0113] When the current is applied to the armature coils 212, and thephase thereof is so controlled as to induce the magnets 231 of the innerrotor 230 to produce a maximum motor torque to rotate the outer andinner rotors 220 and 230 in the normal direction of rotation from theangular position as illustrated in FIG. 12, the magnetic torquesoriented to the reverse direction of rotation (i.e., thecounterclockwise direction in FIG. 12) are first exerted on the outerand inner rotors 220 and 230 for a short period of time. This causes theouter rotor 220 to rotate in the counterclockwise direction, however, anangular shift of the outer rotor 220 immediately after the start-up issmall because the inertial mass of the outer rotor 220 is greater (seeFIG. 14). The inertial mass of the inner rotor 230 is smaller, so thatthe inner rotor 230 starts to rotate quickly in the normal direction(i.e., the clockwise direction in FIG. 12) the short period of timeafter the start-up. This causes the outer and inner rotors 220 and 230to have a relative angle, as shown in FIG. 15, therebetween. In thisposition, each of the ribs 234-1 of the inner stator support stay 234,as shown in FIG. 15, compresses one of the first elastic members 238through the spacer 249 against the elastic load of |F1−F2| and is heldat an angular position defined by the stopper 248-1.

[0114] In the angular position as illustrated in FIG. 15, when thecurrent is applied to the armature coils 212 with the illustrated phase,the magnets 221 and 231 of the outer and inner rotors 220 and 230produce maximum magnetic torques in the clockwise direction.Specifically, the torques To1 and Ti1, as shown in FIG. 16, acting onthe outer and inner rotors 220 and 230 are oriented in the samedirection, thereby resulting in production of a great resultant torqueT1=To1+Ti1 in a direction in which the multi-rotor synchronous machineis to be rotated. This motor mode of operation is, thus, suitable forassisting in producing a higher output torque when the engine is startedor accelerated.

[0115] After completion of the start-up or acceleration of the engine,the quantity of current to be supplied to the armature coils 212 isdecreased to reduce the torques acting on the outer and inner rotors 220and 230 as a function of a required output torque of the synchronousmachine. When the torque Ti2 acting on the inner rotor 230 drops belowthe elastically produced torque Tf, it will cause the inner rotor 230 torotate relative to the outer rotor 220, so that it returns back to theangular position as illustrated in FIG. 12. The resultant magnetic fluxinterlinking with the armature coils 212, thus, decreases greatly,thereby causing the counterelectromotive force produced in the armaturecoils 212 during rotation of the synchronous machine at high speeds tobe lowered.

[0116] The angular relation between the magnets 221 and 231 in thehigh-speed low-torque motor mode or low-speed low-torque motor mode isshown in FIG. 17. The torques To2 and Ti2 produced on the outer andinner rotors 220 and 230 are shown in FIG. 18. The resultant torque T2is given by |To2−Ti2| where To2>Ti2.

[0117] The operation of the synchronous machine in the generation mode(e.g., a regenerative braking mode of the vehicle) will be describedbelow.

[0118] The generation in a high-speed low-torque mode or a low-speedlow-torque mode is achieved by controlling the phase of the currentflowing through the armature coils 212 as illustrated in FIG. 19. Thiscontrol may be performed by supplying the current to the armature coils212 in addition to the current induced in the armature coils 212 by thetorque transmitted form the engine and the transmission. The resultanttorque T3 is, as shown in FIG. 20, given by the relation of T3=To3−Ti3where To3 is the torque acting on the outer rotor 220, and Ti3 is thetorque acting on the inner rotor 230. Note that the elastically producedtorque Tf is greater than the torque Ti3.

[0119] The switching from the state, as illustrated in FIGS. 19 and 20,to a high-torque generator mode (i.e., a low-speed high-torque generatormode) will be described below.

[0120] When the quantity of current flowing through the armature coils212 is increased while controlling the phase thereof so that the magnets231 of the inner rotor 230 may produce a maximum torque in thecounterclockwise direction, the inner rotor 230, unlike the start-upmode of the engine operation, rotates relative to the outer rotor 220 inthe counterclockwise direction while compressing the second elasticmembers 239, as shown in FIG. 23, thereby causing the torques, as shownin FIG. 24, to be produced. Specifically, the phase and quantity of thecurrent flowing through the armature coils 212 is, as shown in FIG. 21,controlled so as to produce the torques To4 and Ti4, as shown in FIG.22, acting on the outer and inner rotors 220 and 230, like the ones inFIG. 18. Note that the torque Tr is produced by the elastic load F2.

[0121] If the inertial mass of the outer rotor 220 and the inertial massof the inner rotor 230 are defined as Io and Ii, and the angularaccelerations thereof are defined as βo4, and βi4, respectively,relations between the torques and accelerations produced on the outerand inner rotors 220 and 230 may be expressed as

To4−Tr=Io·βo4

Ti4−Tr=Ii·βi4

[0122] Since the inertial mass Io of the outer rotor 220 is much greaterthan the inertial mass Ii of the inner rotor 230, the inner rotor 230starts to rotate more quickly than the outer rotor 220. Specifically,the ribs 234-1 of the inner rotor support stay 234 is urged by thecounterclockwise torque Ti4 to compress the second elastic members 239against the elastic load F2 produced by the second elastic members 239and rotates to the angular position defined by the stoppers 248-2. Thecontrolling the current, as shown in FIG. 23, to flow through thearmature coils 212, causes the torques To5 and Ti5 to be produced, asshown in FIG. 24, on the outer and inner rotors 220 and 230,respectively. This causes the resultant toque T5=To5+Ti5 to be produced,thereby achieving the high-torque generation mode.

[0123]FIG. 25 is a flowchart of a program to be performed to operate themulti-rotor synchronous machine in the motor mode at the start-up of theengine. An inverter used to supply the current to the armature coils 212is installed in the controller 500 and has a know structure in which atotal of six three-phase switching elements are installed on an upperand a lower arms and turned on and off selectively in a given sequenceby a controller. The structure and operation of such an inverter isknown in the art, and explanation thereof in detail will be omittedhere.

[0124] When it is required to start the engine, the routine proceeds tostep 102 wherein it is determined whether the relative angle θ betweenthe outer and inner rotors 220 and 230 is zero (0) or not. The relativeangle θ is determined by executing an interrupt routine (not shown) tomonitor the angular positions of the outer and inner rotors 220 and 230through the angle sensor 291 and calculating a difference therebetween.The fact that the relative angle θ is zero (0) means that the inner andouter rotors 220 and 230 are in the neutral position as illustrated inFIGS. 9 and 10.

[0125] If a YES answer is obtained meaning that the inner and outerrotors 220 and 230 are in the neutral position, then the routineproceeds to step 104 wherein the current of phase, as shown in FIG. 12,is supplied to the armature coils 212 to produce a maximum torque actingon the inner rotor 230 that is smaller in inertial mass than the outerrotor 220, thereby shifting the relative angle θ between the inner andouter rotors 220 and 230 through +π, as shown in FIG. 15, so that thesum of magnetic fluxes interlining with the inner and outer rotors 220and 230 may be maximized.

[0126] The routine proceeds to step 106 wherein it is determined whetherthe relative angle θ has reached +π or not. If a NO answer is obtained,then the routine returns back to step 104. Alternatively, if a YESanswer is obtained, then the routine proceeds to step 108 wherein thecurrent of phase, as shown in FIG. 15 is supplied to the armature coils212 to produce the maximum torque T1 in the normal direction of rotationof the synchronous machine which is required to star up the engine.

[0127] The routine proceeds to step 110 wherein it is determined whetherthe engine has been started or not. If a NO answer is obtained, then theroutine returns back to step 108. Alternatively, if a YES answer isobtained, then the routine proceeds to step 112 wherein the supply ofcurrent to the armature coils 212 for producing the maximum motor torqueis stopped and returns back to a main routine (not shown).

[0128]FIG. 26 shows a program to be performed to operate the multi-rotorsynchronous machine in a regenerative braking mode.

[0129] when it is required to operate the multi-rotor synchronousmachine as a generator during braking of the vehicle, the routineproceeds to step 122 wherein the relative angle θ between the outer andinner rotors 220 and 230 is calculated in the same manner as in step 102in FIG. 25 to determine whether the relative angle θ is zero (0) or not.If a NO answer is obtained, then the routine proceeds directly to step126. Alternatively, if a YES answer is obtained, then the routineproceeds to step 124 wherein the phase and quantity of current flowingthrough the armature coils 212 is, as shown in FIG. 21, controlled so asto produce a maximum torque acting on the inner rotor 230 in thecounterclockwise direction to shift the relative angle θ between theinner and outer rotors 220 and 230 through −π, as shown in FIG. 23, sothat the sum of magnetic fluxes interlining with the inner and outerrotors 220 and 230 may be maximized.

[0130] The routine proceeds to step 126 wherein it is determined whetherthe relative angle θ has reached −π or not. If a NO answer is obtained,then the routine returns back to step 124. Alternatively, if a YESanswer is obtained, then the routine proceeds to step 128 wherein thephase and quantity of current flowing through the armature coils 212 iscontrolled so that a the maximum torque T5 may act on the inner andouter rotors 220 and 230 in the reverse direction of rotation.

[0131] The routine proceeds to step 130 wherein it is determined whetherthe regenerative braking command is released or not. If a NO answer isobtained, then the routine returns back to step 128. Alternatively, if aYES answer is obtained, then the routine proceeds to step 132 whereinthe production of the torque in step 128 is stopped and returns back toa main routine (not shown).

[0132] The above program as illustrated in the flowchart of FIG. 25refers only to control of the operation of the multi-rotor synchronousmachine in the start-up mode of the engine operation, however, themulti-rotor synchronous machine of this embodiment may also be usedunder similar control for assisting in producing the output torqueduring rotation of the engine at high speeds.

[0133] The permanent magnet field poles may also be provided on eitherof the outer rotor 220 and the inner rotor 230. For example, the magnets231 of the inner rotor 230 may be replaced with iron plates. In thiscase, the outer rotor 220 acts electromagnetically with the magnet 221,while the inner rotor 230 works to produce the reluctance torque inrelation to the magnetic poles of the iron plates 231.

[0134]FIG. 27 shows a multi-rotor synchronous machine according to thethird embodiment of the invention. The same reference numbers asemployed in the above embodiments will refer to the same parts, andexplanation thereof in detail will be omitted here.

[0135] The multi-rotor synchronous machine of this embodiment hassubstantially the same structure as described in the second embodiment.Specifically, stator windings 212 (i.e., armature coils) are arrayed ina magnetic core 211 of a stator 210. Each stator winding 212 consists ofa conductor shaped to form a number of loops or turns each of whichextends from a front surface of the magnetic core 211 into one of slots213′ perpendicular to the drawing of FIG. 27, passes over a back surfaceof the core back 215, enters one of slots 213, and returns back to afront surface of the magnetic core 211. The armature coils 212 arrayedat a three-slot interval away from each other are coupled to form one ofthree-phase windings.

[0136] The multi-rotor synchronous machine also includes an outer rotor220 and an inner rotor 230. Magnets 221 and 231 are secured on the outerand inner rotors 220 and 230.

[0137] A rotor support stay 240 is connected to a crankshaft 110 of theengine. A magnetic core 211 is installed on a stator support stay 250through a pin 252. The stator support stay 250 is connected to an engineframe or transmission (not shown). An inner rotor support stay 234 whichretains the inner rotor 230 is carried by bearings 235 and 236 to beslidable along the rotor support stay 240.

[0138] An elastic member 238 such as a coil spring is disposed aroundthe inside periphery of the rotor support stay 240. The elastic member239 is secured at one end thereof to the protrusion or rib 240-1 formedon the inside periphery of the rotor support stay 240 and at the otherend thereof to the protrusion or rib 234-1 formed on the inner peripheryof the inner rotor support stray 234.

[0139] The operation of the multi-rotor synchronous machine used as anautomotive generator/motor will be described below. The relation betweenthe speed of the synchronous machine and the produced torque isillustrated in FIG. 28.

[0140]FIG. 29 illustrates the state of the internal structural elementsof the multi-rotor synchronous machine operating in a low-speedhigh-torque motor mode. The magnets 221 of the outer rotor 220 has arelative angle of zero (0) to the magnets 231 of the inner rotor 230.The magnetic flux produced by the magnets 221 of the outer rotor 220 sointerlinks with the armature coils 212 as to produce a maximum torque.The relation between torques produced on the outer and inner rotors 220and 230 and the phase of current flowing through the armature coils 212is shown in FIG. 5.

[0141]FIG. 30 shows the state of the internal structural elements of themulti-rotor synchronous machine operating in a high-speed low-torquemotor mode. The magnets 221 of the outer rotor 220 are shifted inangular position from the magnets 231 of the inner rotor 230 so as todecrease the resultant magnetic flux interlinking with the armaturecoils 212, thereby resulting in a decrease in output torque, as shown inFIG. 4. The decrease in resultant magnetic flux causes the counterelectromotive force produced in the armature coils 212 during rotationof the synchronous machine at high speeds to be reduced.

[0142]FIG. 31 shows the state of the internal structural elements of themulti-rotor synchronous machine operating in a high-speed low-torquegenerator mode. The relative angle between the magnets 221 of the outerrotor 220 and the magnets 231 of the inner rotor 230 is shifted 2π fromthe one shown in FIG. 29. The resultant magnetic flux interlinking withthe armature coils 212 is, like FIG. 29, maximized, thus causing thetorque acting on the outer and inner rotors 220 and 230 to be maximized.This mode is suitable for the regenerative braking.

[0143] The switching from the high-speed low-torque motor mode to thelow-speed high-torque generator mode will be described below.

[0144] In the high-speed low-torque motor mode, the magnets 221 of theouter rotor 220 and the magnets 231 of the inner rotor 230 have thepositional relation as illustrated in FIG. 30. The elastic member 238 islaid, like the one shown in FIG. 27, between the ribs 240-1 and 234-1without undergoing compression and expansion.

[0145] The switching from the state as illustrated in FIG. 30 to thelow-speed high-torque generator mode is accomplished by controlling thephase and quantity of current flowing through the armature coils 212 soas to produce a maximum torque through the magnets 231 of the innerrotor 230 which compresses the elastic member 238, thereby causing themagnets 221 of the outer rotor 220 and the magnets 231 of the innerrotor 230 to have a relative angle as illustrated in FIG. 31. The changein current flowing through the armature coils 212 causes the torqueproduced by the magnets 221 of the outer rotor 220 to change, however,the pressure produced by the outer rotor 220 to compress the elasticmember 238 is lower because of a difference in inertial mass between theouter rotor 220 and the inner rotor 230, so that the elastic member 238contracts or expands mainly depending upon a change in torque producedby the magnets 231 of the inner rotor 230.

[0146] The switching from the high-speed low-torque motor mode to thelow-speed high-torque motor mode will be described below which may beperformed when it is required to assist in producing the output torqueduring rotation of the engine at low speeds.

[0147] The switching to the low-speed high-torque motor mode isaccomplished by supplying the current to the armature coils 212 whichhas the phase to induce a magnetic force greater than the elasticpressure produced by the elastic member 238, thereby moving the innerrotor 230 relative to the outer rotor 220 to expand the elastic member238 until the rib 234-1 of the inner rotor support stay 234 hits, asshown in FIG. 29, on the rib 240-2 of the rotor support stay 240. Thiscontrol is performed when the engine speed is deceased, thus keeping thecounterelectromotive voltage below an allowable level.

[0148] The relation between the amount of expansion of the elasticmember 238 and the load acting on the elastic member 238 is representedin FIG. 32.

[0149] FIGS. 33 to 37 show a multi-rotor synchronous machine accordingto the fourth embodiment of the invention which is different from theone of the third embodiment only in an outer rotor-to-inner rotorrelative angle adjusting structure. Other arrangements are identical,and explanation thereof in detail will be omitted here.

[0150] The inner rotor 230 and the inner rotor support stay 234 aresupported on the rotor support stay 240 rotatably.

[0151] The outer rotor-to-inner rotor relative angle adjusting structureis shown in FIG. 34 which is a sectional view developed in acircumferential direction of the multi-rotor synchronous machine.

[0152] Elastic members 238-1 and 238-2 are, like the above embodiments,disposed between the inner rotor support stay 234 and the rotor supportstay 240. The elastic member 238-1 is in engagement at one end thereofwith the rib 234-2 formed on the inner periphery of the inner rotorsupport stay 234 and at the other end thereof with the spacer 237. Theelastic member 238-2 is in engagement at one end thereof with the rib240-3 formed on the outer periphery of the rotor support stay 240 and atthe other end thereof with the rib 234-3 formed on the inner peripheryof the inner rotor support stay 234.

[0153] When not subjected to any load, the elastic members 238-1 and238-2 are held at an angular position in which the rib 234-4 formed onthe inner periphery of the inner rotor support stay 234 is in alignmentwith the rib 240-3 on the rotor support stay 240. In this position, theelastic pressure f1 produced by the elastic member 238-1 and the elasticpressure f2 produced by the elastic member 238-2 meet a relation off1≧f2.

[0154] The switching from a low torque mode to a high torque mode ofoperation of the multi-rotor synchronous machine will be describedbelow.

[0155] In the generation mode of operation of the multi-rotorsynchronous machine, the phase of current flowing through the armaturecoils 212 is controlled to produce on the inner rotor 230 the torque ina direction reverse to rotation thereof which is greater than aresultant pressure |f1−f2| of the elastic members 238-1 and 238-2,thereby causing, as shown in FIG. 35, the elastic member 238-1 to becompressed and the elastic member 238-2 to be expanded, so that theangular interval between the rib 240-3 of the rotor support stay 240 andthe rib 234-2 of the inner rotor support stay 234 is decreased. Themagnets 221 of the outer rotor 220 has a positional relation to themagnets 231 of the inner rotor 230 which creates a maximum magnetic fluxinterlinking with the armature coils 212, producing a maximum torque inthe reverse direction (i.e., the counterclockwise direction as viewed inFIG. 35).

[0156] In the motor mode, the phase of current supplied to the armaturecoils 212 is so controlled as to produce the torque which is greaterthan the elastic pressure of the elastic member 238-2 on the inner rotor230 in the same direction as that in which the synchronous machine is tobe rotated, thereby causing, as shown in FIG. 36, the elastic member238-2 to be compressed, so that the angular interval between the rib240-3 of the rotor support stay 240 and the rib 234-3 of the inner rotorsupport stay 234 is decreased. Both the magnetic flux produced by themagnets 221 of the outer rotor 220 and the magnetic flux produced by themagnets 231 of the inner rotor 230 interlinking with the armature coils212 are maximized, thereby producing a maximum torque in the directionin which the synchronous machine is to be rotated (i.e., the clockwisedirection as viewed in FIG. 36).

[0157] The relation between the amount of expansion of the elasticmembers 238-1 and 238-2 and the produced torque is shown in FIG. 37.

[0158] In the above embodiments, the outer and inner rotors 220 and 230are arranged coaxially with each other, however, they may alternativelybe arrayed tandem in the axial direction of the synchronous machine in atandem.

[0159] In the second to fourth embodiments, when no current flowsthrough the armature coils 212, the center of each magnet on the outerrotor 220 is in alignment with the center of one of the magnets on theinner rotor 230 in a radial direction, however, they may alternativelybe shifted in angular position from each other.

[0160]FIG. 38 shows the part of an automotive power train according tothe fifth embodiment of the invention in which a multi-rotor synchronousmachine is installed as a generator/motor.

[0161] The generator/motor 5 is disposed in a housing 3 and coupled witha front surface of a flywheel 2. The flywheel 2 is secured to acrankshaft 110 leading to an internal combustion engine of the vehicle.The crankshaft 110 is connected at a rear end thereof to an input shaft6 of a reduction gear mechanism or transmission in alignment therewiththrough a bearing 7. The input shaft 6 passes through the center of theflywheel 2 and connects with the crankshaft 110.

[0162] The flywheel 2 is secured to the rear end of the crankshaft 110through bolts. The flywheel 2 is made up of a small-diameter cylinder 21joined to the flywheel 2, a large-diameter cylinder 23 lying coaxiallywith the small-diameter cylinder 21, and a disc 22 extending radially toconnect rear ends of the small-diameter and large-diameter cylinders 21and 23. The small-diameter cylinder 21 has an opening 24 and a groove 25formed in a rear end thereof.

[0163] A mechanical clutch 4 is fitted on the input shaft 6. Themechanical clutch 4 includes a clutch plate 41, a pressure plate 42, aclutch spring 43, a clutch cover 44, and a hydraulic pressure releasingmechanism 45.

[0164] The clutch plate 41 includes a hollow cylinder 411, a disc 412,and a clutch damper 413. The cylinder 411 has a recess 410 formedtherein and is fitted on the input shaft 6 nonrotatably yet slidably ina lengthwise direction of the input shaft 6. The disc 412 extends from arear end of the cylinder 411 to the rear end surface of the flywheel 2.The clutch damper 413 is disposed between the cylinder 411 and the disc412 to connect them together and works to absorb a change in torque.

[0165] The disc 412 includes a frictional disc 414 which is engageblewith the rear end surface of the flywheel 2. The clutch damper 413 ismade of a rubber ring or a coil spring which extends around the cylinder411 and is engagement at one end with the cylinder 411 and at the otherend with the disc 412 so that it may be elastically deformed by a cyclicchange in transmitted torque to absorb it. The clutch damper 413 isdisposed at a front portion thereof in the groove 25 formed in thesmall-diameter cylinder 21 of the flywheel 2.

[0166] The pressure plate 42 is made of an annular plate and is placedin engagement with the rear end of the clutch plate 41. The pressureplate 42 is supported at an outer periphery thereof by the clutch cover44 secured to on an outer end portion of the flywheel 2.

[0167] The clutch spring 43 is made of a disc plate which is deformablein the axial direction of the input shaft 6. The clutch spring 43 is inclose engagement at an outer periphery thereof with the rear end surfaceof the pressure plate 42 and fitted at an inner periphery thereof, asclearly shown in FIG. 39, in the hydraulic pressure releasing mechanism45 to be non-slidable backward. The clutch spring 43 is also in contactat a portion inside the outer periphery joined to the pressure plate 42with an inner edge of the clutch cover 44. In the steady state, theclutch spring 43 is deformed in the axial direction of the input shaft 6to urge the clutch plate 41 into constant engagement with the rear endsurface of the flywheel 2 through the pressure plate 42, therebyestablishing a connection of the flywheel 2 to the input shaft 6.

[0168] The hydraulic pressure releasing mechanism 45 includes a sleeve451, a release piston 452, and a release bearing 453. The sleeve 451 isinstalled on a barrier plate 30 of the housing 3 and fitted on the inputshaft 6 with a given play. The barrier plate 30 defines a reduction gearchamber and a clutch chamber. The release piston 452 is installed on thesleeve 451 to be slidable in the axial direction of the sleeve 451. Therelease bearing 453 is installed on the periphery of the release piston452. The sleeve 451 and the release piston 452 define a hydraulicchamber 454 therebetween. The release bearing 453 is in engagement at anouter race thereof with the inner periphery of the clutch spring 43.

[0169] The disengagement of the clutch 4 is accomplished by supplyingthe hydraulic pressure into the hydraulic chamber 454 to advance therelease piston 452 and the release bearing 453 together, so that theouter race of the release bearing 453 moves the inner periphery of theclutch spring 43 forward, thereby causing the outer periphery of theclutch spring 43 to move backward. This causes the pressure plate 42 tomove backward because of the tight engagement of the outer periphery ofthe pressure plate 42 with the outer periphery of the clutch spring 43.The pressure urging the clutch plate 41 into constant engagement withthe flywheel 2, thus, disappears, thereby releasing the engagement ofthe flywheel 2 with the input shaft 6.

[0170] The engagement of the clutch 4 is accomplished by releasing thehydraulic pressure from the hydraulic chamber 454 to produce thepressure urging the pressure plate 42 into constant engagement with theflywheel 2 through the clutch plate 41, which establishes the connectionof the flywheel 2 to the input shaft 6.

[0171] The generator/motor 5 includes an outer rotor 220, an inner rotor230, and a stator 210. The outer rotor 220 is installed on the innerperiphery of the large-diameter cylinder 23 of the flywheel 2. The innerrotor 230 is installed on the outer periphery of the small-diametercylinder 21 of the flywheel 2. The stator 210 is disposed between theinner rotor 230 and the outer rotor 220.

[0172] The inner rotor 230 includes a yoke 521 on which permanentmagnets 512 are installed. The outer rotor 220 includes a yoke 521 onwhich permanent magnets 522 are installed. The stator 210 includes airon core 531 in which armature coils 532 are installed. The armaturecoils 532 are each made up of a conductor shaped in a toroidal form. Theiron core 531 is installed on the housing 3. In the motor mode ofoperation of the generator/motor, the supply of current to the armaturecoils 532 causes the outer and inner rotors 220 and 230 to rotate toproduce the torque acting on the crankshaft 1. In the generator mode,the torque is transmitted from the crankshaft 1 to the outer and innerrotors 220 and 230, thereby inducing the current in the armature coils532.

[0173] As apparent from the above discussion, the release piston 452 andthe release bearing 453 are disposed ahead of the clutch spring 43. Theclutch spring 42 is designed to be hydraulically urged forward throughthe release bearing 452 to disengage the clutch 4. This eliminates theneed for defining a chamber required to install hydraulic pressurereleasing mechanism behind the clutch spring 43, thus allowing theoverall length of the power train to be decreased as compared with aconventional structure in which a hydraulic pressure releasing mechanismis installed behind a clutch spring.

[0174] Additionally, the release bearing 453 is fitted on the releasepiston 452, thus allowing the length of the power train to be decreasedby an amount equivalent to the thickness of the release bearing 453 ascompared with the conventional structure. Further, the release bearing453 does not face the clutch plate 41 through the release piston 452,thus allowing a required interval between the outer race of the releasebearing 453 and the inner periphery of the clutch plate 41 in the axialdirection of the power train to be decreased, which allows the releasebearing 453 to urge the clutch plate 41 into constant engagement withthe flywheel 2 through the pressure plate 42 under a decreased elasticpressure.

[0175] The generator/motor 5 may alternatively have any of thestructures of the above described first to fourth embodiments.

[0176] While the present invention has been disclosed in terms of thepreferred embodiments in order to facilitate better understandingthereof, it should be appreciated that the invention can be embodied invarious ways without departing from the principle of the invention.Therefore, the invention should be understood to include all possibleembodiments and modifications to the shown embodiments witch can beembodied without departing from the principle of the invention as setforth in the appended claims.

What is claimed is:
 1. A multi-rotor synchronous machine comprising: afist rotor having permanent magnet field poles, secured to an outputmember; a second rotor having permanent magnet field poles, disposed tobe rotatable relative to said first rotor; a stator core having armaturecoils interlinking with field magnetic fluxes produced by the permanentmagnet field poles of said first and second rotors; and a rotor-to-rotorrelative rotation controlling mechanism designed to allow said secondrotor to rotate relative to said first rotor within a given angularrange and prohibit said second rotor from rotating out of the givenangular range.
 2. A multi-rotor synchronous machine as set forth inclaim 1, wherein said rotor-to-rotor relative rotation controllingmechanism includes a first stopper working to limit rotation of saidsecond rotor relative to said first rotor in a first direction over afirst angular range and a second stopper working to limit rotation ofsaid second rotor relative to said first rotor in a second directionopposite the first direction over a second angular range.
 3. Amulti-rotor synchronous machine as set forth in claim 2, wherein saidrotor-to-rotor relative rotation controlling mechanism includes anelastic member which is engagement at one end thereof with said firstrotor and at the other end with said second rotor to urge said first andsecond rotors in opposite directions.
 4. A multi-rotor synchronousmachine as set forth in claim 1, wherein said stator core is made of ahollow cylindrical member, and wherein said first rotor and said secondrotor are disposed coaxially with an outer and an inner periphery ofsaid stator core, respectively.
 5. A multi-rotor synchronous machine asset forth in claim 4, wherein said second rotor is disposed inside theinner periphery of said stator core, and wherein said rotor-to-rotorrelative rotation controlling mechanism is installed inside said secondrotor.
 6. A multi-rotor synchronous machine as set forth in claim 1,wherein rotation of said second rotor relative to said first rotor isaccomplished by controlling at least one of phase and quantity ofcurrent flowing through the armature coils of said stator core.
 7. Amulti-rotor synchronous machine comprising: a pair of rotors at leastone of which has permanent magnet field poles, said rotors being arrayedcoaxially to be rotatable relative to each other; a stator core;armature coils wound in said stator core, interlining with a field fluxproduced by said rotors; a sensor measuring a relative angle betweensaid rotors; and a rotor-to-rotor relative angle controller working toestablish a relative rotation between said rotors to change the relativeangle measured by said sensor to a target angle.
 8. A multi-rotorsynchronous machine as set forth in claim 7, wherein said stator core ismade of a hollow cylindrical member, wherein said rotors are an outerrotor disposed around an outer periphery of said stator core and aninner rotor disposed around an inner periphery of said stator core, andwherein said rotor-to-rotor relative angle controller includes arelative rotation controlling mechanism disposed inside said inner rotorfor controlling a relative rotation between said rotors.
 9. Amulti-rotor synchronous machine as set forth in claim 8, wherein saidrelative rotation controlling mechanism includes an elastic member laidbetween said rotors in a circumferential direction thereof to keep saidrotors in a neutral position, and wherein said rotor-to-rotor relativeangle controller changes magnetic torques acting on said rotors toadjust a relative angle between said rotors to a target angle.
 10. Amulti-rotor synchronous machine as set forth in claim 9, wherein saidrotor-to-rotor relative angle controller is designed to change themagnetic torque acting on said rotors to rotate one of said rotorsrelative to the other from the neutral position while compressing orexpanding said elastic member, thereby adjusting the relative anglebetween said rotors to the target angle.
 11. A multi-rotor synchronousmachine as set forth in claim 9, wherein said relative rotationcontrolling mechanism includes a pair of elastic members secured on oneof said rotors to establish the neutral position in which said rotorshave a preselected angular relation therebetween when the armature coilsis deenergized, and wherein said rotor-to-rotor relative anglecontroller changes the magnetic torques acting on said rotor to causeone of the elastic members to be compressed while expanding the otherelastic member, thereby adjusting the relative angle between said rotorsto the target angle.
 12. A multi-rotor synchronous machine as set forthin claim 10, wherein said relative rotation controlling mechanismincludes a pair of stoppers working to define a relative rotationallowable range of said rotors.
 13. A multi-rotor synchronous machine asset forth in claim 12, wherein when said rotors are in a first relativeangular position lying one of limits of the relative rotation allowablerange defined by one of the stopper, a maximum torque is produced onsaid rotors in a direction of rotation of the multi-rotor synchronousmachine, when said rotors are in a second relative angular positionlying the other limit of the relative rotation allowable range definedby the other stopper, a maximum torque being produced on said rotors ina direction reverse to the direction of rotation of the multi-rotorsynchronous machine.
 14. A multi-rotor synchronous machine as set forthin claim 7, wherein one of said rotors has an inertial mass two timesgreater than that of the other rotor or more.
 15. A multi-rotorsynchronous machine as set forth in claim 14, wherein one of said rotorshaving the greater inertial mass is coupled to a crankshaft of anautomotive engine, and the other rotor is coupled to the one of saidrotors through said rotor-to-rotor relative angle controller to berotatable relative to the one of said rotors.
 16. A multi-rotorsynchronous machine as set forth in claim 9, wherein the relativerotation controlling mechanism establish an engagement between saidrotors so as to allow said rotors to rotate relative to each othercontinuously in a given angular range.
 17. A drive apparatus for anautomotive vehicle comprising: a flywheel connected to a rear end of acrankshaft of an engine; a generator/motor includes a stator which islocated in front of said flywheel and secured to a housing and a rotorwhich is secured on said flywheel and faces a peripheral surface of thestator; and a mechanical clutch establishing an engagement between saidflywheel and an input shaft of a gear reduction unit disposed behindsaid flywheel, the input shaft extending through said flywheel coaxiallywith the crankshaft, said mechanical clutch including, (a) a pressureplate supported by said flywheel nonrotatably and slidably in an axialdirection of the input shaft of the gear reduction unit, said pressureplate facing a rear surface of said flywheel through a given gap, (b) aclutch plate supported by said input shaft nonrotatably and slidably inthe axial direction, said clutch plate being disposed between the rearsurface of said flywheel and a front surface of said pressure plate, (c)an annular clutch spring located behind said pressure plate, supportedby said flywheel so as to urge at an outer periphery thereof a rear endsurface of said pressure plate frontward, (d) a sleeve fitted on theinput shaft through a given gap between itself and an outer peripheralsurface of the input shaft, said sleeve being located behind said clutchplate and secured at a rear end thereof to said housing, (e) a releasepiston fitted on the outer peripheral surface of said sleeve slidably inan axial direction of said sleeve, and (f) a release bearing fitted onsaid release piston or said sleeve to be movable in the axial directionto urge an inner peripheral portion of said clutch spring, wherein saidflywheel includes a small-diameter cylinder coupled at a front endthereof to the rear end of said crank shaft and a disc extending from arear end of the small-diameter cylinder in a centrifugal direction to beengageble with said clutch plate, wherein said clutch plate includes acylinder which has a chamber opened rearward into which said releasebearing is allowed to be inserted at least partially and which is fittedon said input shaft nonrotatably and slidably in the axial direction anda disc extending from a rear end of the cylinder between the rear endsurface of said flywheel and the front end surface of said pressureplate, and wherein at least a portion of said release piston and saidrelease bearing are located frontward of said clutch spring.
 18. A driveapparatus as set forth in claim 17, wherein said release bearing isfitted on said release piston.
 19. A drive apparatus as set forth inclaim 18, wherein said clutch plate includes a clutch damper locatedbetween the cylinder and the disc thereof for absorbing a variation intorque, a front portion of said clutch damper being disposed within achamber formed in a rear end portion of the cylinder of said flywheel.